This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for controlling the operation of gas turbine engines.
Gas turbine engines typically include a compressor section, a combustor section, and at least one turbine section. The compressor compresses air, which is mixed with fuel and channeled to the combustor. The mixture is then ignited generating hot combustion gases. The combustion gases are channeled to the turbine, which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to power a load, such as an electrical generator, or to propel an aircraft in flight.
Gas turbine engines operate in many different operating conditions, and combustor performance facilitates engine operation over a wide range of engine operating conditions. Controlling combustor performance may be used to improve overall gas turbine engine operations. More specifically, permitting a larger variation in gas fuel composition, for example, heating value and specific gravity, while maintaining NOx emissions and combustion dynamics levels within predetermined limits. Gas turbines equipped with Dry Low NOx (DLN) combustion systems typically utilize fuel delivery systems that include multi-nozzle, premixed combustors. DLN combustor designs utilize lean premixed combustion to achieve low NOx emissions without using diluents such as water or steam. Lean premixed combustion involves premixing the fuel and air upstream of the combustor flame zone and operation near the lean flammability limit of the fuel to keep peak flame temperatures and NOx production low. To deal with the stability issues inherent in lean premixed combustion and the wide fuel-to-air ratio range that occurs across the gas turbine operating range, DLN combustors typically have multiple fuel nozzles in each combustion chamber that are fueled individually or in sub-groups. The gas turbine fuel system has a separately controlled delivery circuit to supply each group of nozzles in each chamber. The control system varies the fuel flow (fuel split) to each circuit over the turbine operating range to maintain flame stability, low emissions, and acceptable combustor life. Fuel flow to each nozzle sub-group is controlled via a gas control valve (GCV). The fuel split acts to divide the total fuel command (Fuel Stroke Reference) amongst the active GCV's, and the resulting percentage GCV fuel flow command is converted to a valve position to achieve the desired fuel flow to the nozzle sub-group.
Many discrete control systems use third or private party software interface programs to structure and create executable software code. These software interfaces can limit the software structure flexibility, are generally more focused on Boolean or logic based software strategies, and often are not suited for nested loop or matrix-based software. Some digital control system platforms do not directly allow loop (if, while, etc) based software, and do not allow for dynamically expandable matrices, therefore all matrix dimensions specified at variable creation are fixed. Such restrictions create several challenges when implementing an iterative matrix based fluid system flow model.